Filter assembly

ABSTRACT

A filter assembly for an additive manufacturing apparatus has a housing defining a gas inlet and a gas outlet. A filter element is located within the housing between the gas inlet and the gas outlet. The assembly includes valves that can be actuated to seal the gas inlet and the gas outlet. Additionally the assembly has a fluid inlet for allowing ingress of a fluid into the housing. The assembly allows a filter element, which may contain volatile particles, to be changed safely. By sealing the gas inlet and outlet and flooding the housing with a suitable fluid, volatile particles captured by the filter can be neutralised.

BACKGROUND TO THE INVENTION

Additive manufacturing, rapid manufacturing or rapid prototyping methodsfor producing three-dimensional components are well known in the art(see for example U.S. Pat. No. 4,863,538—Deckard). There are variousknown methods of additive manufacturing including consolidation ofpowder materials and curing of polymeric resins (Stereolithography-SLA).SLM and SLS manufacturing methods involve a layer-by-layer consolidationof powder material using a focused energy beam, such as a laser beam oran electronbeam.

In a typical selective SLS or SLM process, a thin layer of powder isdeposited over a build area or powder bed within a SLS or SLM apparatus.A focused laser beam is scanned across portions of the powder layer thatcorrespond to a cross-section of the three-dimensional article beingconstructed such that the powder at the points where the laser scans isconsolidated either by sintering or by fusion. The cross-sectiontypically generated from a 3-D description of the component generated byscanning an original component or from computer-aided design (CAD) data.

After consolidation of a layer, the build surface is lowered by thethickness of the newly consolidated layer and a further layer of powderis spread over the surface. Again, the surface is irradiated with alaser beam in portions of the layer that correspond to a cross-sectionof the three-dimensional article, the newly consolidated layer beingjoined to the initial consolidated layer. This process is repeated untilthe component is completed.

When operating an additive manufacturing apparatus as described above ahigh powered laser heats the powder beyond its melting point resultingin formation of metal vapour in the atmosphere above the build surface.This metal vapour subsequently condenses forming powders with extremelysmall diameter e.g. diameters below 1 micron. At these diameters powdersof most material types, particularly metals such as titanium, are highlyreactive and liable to spontaneously combust on contact with air. Thecondensates usually appear as a “smoke” in the region above the buildsurface (build chamber) and some of this smoke is removed from the buildchamber by a flow of inert gas through the build chamber.

Although it is relatively easy to trap such fine condensates within afilter element arranged in-line with the gas flow (where the collectedresidue resembles soot) there a significant safety problem with thereactivity of the condensates. When changing filters, extreme care mustbe taken to prevent fires igniting within the filters on contact withair. Although a fire within a filter is a small fire, any fire near anapparatus containing metal powder or in a facility containing metalpowder may act as to ignite a much larger and potentially serious fire.Therefore, deposits need to be treated with great care and collected ina safe manner in an inert atmosphere before being neutralized.

A prior art method of removing a used filter element from a filterassembly on an additive manufacturing machine involves the withdrawal ofthe filter element into a polythene bag associated with the filterassembly. The bag is then manually tied at two points on its lengthbetween the removed filter element and the filter assembly and cutbetween these two sealed points to remove the filter element withoutexposure to air. The bag containing the filter element is then placed inan airtight container and removed from the site to be disposed of. Thisprior art method leaves much room for human error, for example in safesealing of the bag as it is removed.

SUMMARY OF INVENTION

The invention defines a filter assembly, an additive manufacturingapparatus and a method according to the appended independent claims towhich reference should now be made. Preferred or advantageous featuresof the invention are defined in dependent sub-claims.

In the first aspect the invention may provide a filter assembly, whichmay be termed a safe change filter assembly, for removing particulatesfrom a gas stream. Preferably the filter assembly is for an additivemanufacturing apparatus such as an SLM or SLS apparatus. The assemblycomprises a filter housing having a gas inlet, gas outlet, and means forremovably locating a filter element within the housing between the gasinlet and gas outlet. The filter assembly can be mounted in-line in agas flow of an apparatus such that the filter element can filterparticles from the gas. The assembly further comprises a valveactuatable to seal the gas inlet, a valve actuatable to seal the gasoutlet and a fluid inlet for allowing ingress of a fluid into thehousing. The fluid inlet is for allowing ingress of a fluid, preferablya neutralizing fluid such as water, into the housing when the gas inletand gas outlet valves have been sealed. The fluid inlet may have anassociated valve to close the fluid inlet when the filter assembly is inuse on an apparatus.

This filter assembly advantageously allows the fluid to displace the gassealed within the housing when the valves of the gas inlet and gasoutlet have been closed, and allows neutralization of any volatile orexplosive particulate matter within the filter housing.

Preferably the filter assembly is removably-mountable to an additivemanufacturing apparatus, for example an SLM or SLS apparatus. Thismounting may be achieved by means of quick release couplings at the gasinlet and the gas outlet which couple with pipes of a gas flow circuitof the apparatus. Any suitable means for coupling the assembly to a gasflow circuit could be used, for example screw fittings.

Advantageously, a removable filter assembly allows element containingpotentially volatile explosive particles to be sealed from the gas flow(by means of the valves at the gas inlet and gas outlet) and thenremoved from the vicinity of the apparatus for further processing.

The assembly may comprise a fluid outlet for allowing egress of fluidfrom the housing. Such an outlet is particularly advantage us wherewater is used as a neutralizing fluid. Water can be pumped into thehousing via the fluid inlet and allowed to continuously flow into thehousing, simultaneously draining via the outlet. Potentially dangerousparticulate matter may be removed from the housing in a safe state bythe flow of liquid. Advantageously, a fluid outlet may allow gas withinthe housing to escape the housing when fluid is added through the inlet.A hose connection may transport such gas to escape beneath a layer ofliquid so that any particulate matter in the gas is trapped in theliquid and does not escape to air.

If there is no fluid outlet then it preferably that the housingincorporates some form of vent to facilitate release of gas from thehousing when it is flooded with fluid.

Preferably the filter housing is divided into two sections by the filterelement. I.e. there is preferably an upstream section that receives acontaminated gas flow from a gas inlet on one side of the filter elementand a downstream section containing gas that has passed through thefilter element on the other side of the filter element. Thus, it may beadvantageous in this situation to have a first fluid inlet allowingingress of the fluid to the upstream section of the housing and a secondfluid inlet allowing fluid ingress to the downstream section of thehousing. The use of two inlets arranged in this manner may make theprocess of neutralizing the contaminated filter element by the fluidmore efficient and more quickly achievable.

An assembly having a housing with an upstream section and a downstreamsection and first and second fluid inlets as described above mayadvantageously have first and second fluid outlets servicing bothupstream and downstream sections of the housing (if a continuous flow offluid is to be used to neutralize the particulate matter).

Preferably the filter assembly is arranged to receive a cylindricalfilter element. Such filter elements are standard components forfiltering purposes in many industries and particularly in automotiveuse. The assembly may be arranged with location members to fit thefilter element within the housing, for example a spigot surrounding thegas outlet for receiving the open end of a cylindrical filter element.

Advantageously the housing may comprise a flow diverter for directinggas flow from the gas inlet to the filter element. Such a diverter is aparticular advantage where the filter element is a cylindrical filterelement. A gas diverter allows the gas stream to be diverted to thesides of a cylindrical filter element where it can pass directly throughthe filtering material.

The housing comprises means for removably locating a filter element.Advantageously the housing may be a modular housing having two separateportions. A first portion or upper portion may comprise the gas inletand a second portion or lower portion may comprise the gas outlet. Insuch a case the first portion and the second portion would beopenably-couplable to form the housing. The use of a two-part housing asdescribed above allows access to a filter element located within thehousing to replace the filter element, i.e. by separating the twoportions of the housing. Preferably the act of coupling the two housingportions clamps a filter element between the portions and thus assistsin its location within the housing.

In a further aspect the invention may provide an additive manufacturingapparatus for example an SLM or SLS apparatus comprising a filterassembly as described above. Such an additive manufacturing apparatusmay have a build chamber for building an article and a gas flow circuitor gas flow circuits for passing a flow of gas through the buildchamber, thereby removing particulate matter generated during themanufacturing process.

The apparatus preferably comprises a filter assembly or assemblies asdescribed above arranged to be in-line with the or each gas flowcircuit. Advantageously the or each gas flow circuit may comprise avalve that is actuatable to seal the circuit upstream from the filterassembly prior to removal of the filter assembly from the apparatus.Likewise the or each gas flow circuit a ay further comprise a valveactuatable to seal the gas flow circuit downstream from the filterassembly prior to removal of the filter assembly from the apparatus.These additional valves associated with the apparatus may assist inmaintaining the integrity of the gas in the gas flow circuit duringremoval of the filter assembly. Advantageously, this allows one filterassembly to be removed and replaced with a further filter assembly withminimal downtime to the machine.

Advantageously, the apparatus may comprise more than a filter assemblyarranged within a gas flow. For example the apparatus may comprise firstand second filter assemblies arranged in parallel within a gas flowcircuit of the apparatus. This arrangement preferably allows each of thefirst and second filter assemblies to be separately removable from theapparatus to allow filter elements within the first and second filterassemblies to be independently changed. This arrangement may allow thefilter elements within the first and second filter assemblies to bechanged during operation of the apparatus by allowing first a filterelement within the first filter assembly to be changed while the secondfilter assembly is in service, and then a filter element within thesecond filter assembly to be changed while the first is in service. Sucha system may be of considerable advantage during a long manufacturingoperation and may allow the manufacturing operation to be completedwithout interruption for a change of filter.

In a further aspect the invention may provide a method of changing aparticle filter element located within a filter housing mounted to, forexample, an additive manufacturing apparatus. The method comprises thesteps of a) closing a valve to seal a gas inlet to the housing andclosing a valve to seal a valve outlet from the housing therebycompletely sealing the housing, b) removing the housing from theapparatus, c) flooding the housing with a fluid, d) opening the housing,and e) replacing the filter element.

Steps b) and c) can be performed in any order, for example the housingcan be removed from the apparatus and then flooded with the fluid oralternatively can be flooded with a fluid while still attached to theapparatus and then removed from the apparatus. The fluid used to floodthe housing is preferably a neutralizing fluid for neutralizingparticulate material collected on the filtering within the filterhousing. An example of a fluid that is often appropriate is water.

Preferably the filter housing is mounted in-line in a gas flow circuitof the apparatus and the method further comprises steps of closingvalves to seal the gas flow circuit while the filter housing is removedfrom the apparatus.

The step of flooding the housing may comprise the steps of coupling aninlet to a fluid source, for example a source of water opening an inletvalve, and passing fluid into the housing. It may be sufficient to floodthe housing through the inlet and then either directly open the floodedhousing or empty the flooded housing via the inlet before opening thehousing. Alternatively the step of flooding may comprise the step ofopening an outlet valve on a fluid outlet leading from the housing andallowing fluid to pass out of the housing. This additional step mayallow a continuous flow of fluid through the housing. For example, thefilter housing may be connected to a water supply via an inlet and thewater may flow continuously through the housing for a period of timepassing out of the outlet and in the process washing particulate matterfrom the housing. The fluid flow may then be terminated after apredetermined time and the housing then opened, or drained and opened.

Preferred embodiments of the invention will now be described with theaid of Figures in which:

FIG. 1 is a schematic diagram of a selective laser melting apparatusshowing the gas flow circuits for providing gas flow through the buildchamber,

FIG. 2 is a perspective view of a filter assembly embodying theinvention,

FIG. 3 is an illustration showing the filter assembly of FIG. 2 in theprocess of being loaded with a fresh filter element,

FIG. 4 is a perspective View illustrating a pair of filter assembliesembodying the invention mounted in parallel in a gas flow circuit,

FIG. 5 is a schematic diagram illustrating the embodiment of FIG. 4.

FIG. 1 is a diagram illustrating a selective laser melting (SLM)apparatus 10, for example an MTT Technologies SLM 250 machine. Theapparatus has a build chamber 20 providing a controlled atmosphere overa build surface 30. Successive layers of powder are solidified by meansof a laser beam 40 provided from a laser module 50 resulting in thebuild-up of a component 60. The build chamber 20 has a first gas flowinlet 70 for providing a gas shroud over the build surface and a secondgas inlet 80 for providing a protective stream of gas at the roof of thebuild chamber to prevent soot build-up on the laser module 50. Gaspumped into the build chamber via these two inlets 70/80 is exhaustedfrom the build chamber through exhaust 90. The exhausted gas containsparticulate matter entrained in the gas stream as it passes through thebuild chamber.

A pump 100 maintains a flow of gas around the gas flow circuit (i.e. thecircuit entering the build chamber at inlet 70, 80 and exhausted fromthe build chamber through exhaust 90). In addition to the pump, the gasflow circuit has valves for re-directing the gas flow 110, 115, aparticulate filter for removing particulate matter from the gas stream120, and a 12eap filter 130. The filters, valves and pump are arrangedin-line with the gas flow circuit.

The particulate filter 120 comprises a housing containing filter elementfor removal of particulate matter entrained in the gas flow from thebuild chamber.

A filter assembly embodying the invention will now be described withreference to FIGS. 2 and 3.

The assembly has a gas inlet 210 couplable to the gas flow circuitdownstream of the exhaust 90, and a gas outlet 220 downstream from thegas inlet and couplable to the gas flow circuit upstream of the 12eapfilter. The filter assembly comprises a filter housing 230 havingseparable upper 231 and lower 232 portions. The upper portion isillustrated as transparent in FIG. 2 in order to clearly show the filterelement and deflector inside. The housing is substantially cylindricaland the upper portion 231 and the lower portion 232 are securelyclamped, when in use, at clamping rim 233. The clamping rim incorporatesscrews 235 and 235′ for affecting clamping of the two portions and aO-ring for sealing the housing when assembled.

A flow deflector 240 is incorporated in the upper portion 231 of thefilter housing. The flow deflector 240 presses down on the end of anddirects gas flow to the sides of a cylindrical filter element 250. Thefilter element is located by a spigot surrounding the gas outlet in thelower portion 232 of the housing and securely clamped in place bypressure exerted from the flow deflector 240 of the upper portion 231when the housing is assembled.

The assembly has a dirty side water inlet 260 for supplying water to thefilter housing upstream of the filter element (after the filter assemblyhas been sealed from the gas flow circuit). The assembly also has aclean side water inlet 270 on the clean side of the filter element, i.e.downstream of the filter element.

Once the filter element has been sealed by closing the gas inlet valve281 and the gas outlet valve 282, water is pumped into the housing viathe dirty side inlet and the clean side inlet 260, 270 to efficientlyflood the housing on both sides of the filter element 250. This floodingwith water entraps condensate and particulate matter held against thefilter element and within the housing and neutralizes these particles,thereby substantially eliminating the risk of explosion during removalof the filter element.

FIG. 3 illustrates the filter assembly in the process being fitted witha filter element 250. The upper portion 231 has been separated from thelower portion 232 by removing clamping screws in the clamping rim 233.The filter element 250 is in the process of being fitted over a spigotin the lower portion of the housing. FIG. 3 illustrates a gas inletvalve assembly 281 and a gas outlet valve assembly 282 coupled to thehousing to seal the housing from the machine's gas flow circuit prior toremoval from the gas flow circuit and subsequent flooding with water.

FIGS. 4 and 5 illustrate an alternative embodiment of the invention inwhich two filter assemblies are mounted in parallel in-line with the gasflow circuit.

An exhaust manifold 490 transports gas from the build chamber of an SLMapparatus. The exhaust manifold splits the gas flow between two parallellines 491 and 492. These parallel lines each run through a filterassembly 501, 502 and the flow is rejoined into a single line atT-junction 510.

As each flow-line between the exhaust manifold 490 and the T-junction510 has identical components, only one will be described.

On passing into one of the two parallel lines, the gas flow passesthrough a first valve 520. This first valve 520 is actuatable to sealthe gas line, i.e. to prevent further gas flow from the manifold throughthe filter 501.

Downstream from the first valve 520 is the filter assembly 501, whichhas a gas inlet valve 530 actuatable to seal the gas inlet side of thefilter assembly. Gas passing through this gas inlet valve 530 passesinto the filter housing 503 and passes through a filter element 540.

After passing through the filter element 540, the gas flow passesthrough gas outlet valve 550. The gas outlet valve 550 seals the gasoutlet or downstream end of the filter assembly. Gas flow then passesthrough second gas circuit valve 560. The second gas circuit valve 560is actuatable to seal the gas flow circuit from the external environmentwhen the filter assembly is removed from the apparatus.

In between the first gas flow valve 520 and the gas inlet valve 530there is a first quick fit coupling 600. Likewise, between the gasoutlet 550 and the second gas circuit valve 560 there is a second quickfit coupling 610. When the first and second gas circuit valves 520, 560and the gas inlet and gas outlet valves 530, 550 have been closed, thequick fit couplings 600, 610 can be released to allow removal of thefilter assembly from the apparatus.

Although each of the parallel gas lines has the same components, theelements of the lines can be operated independently. Thus, the filterassembly 501 of the first gas line 491 can be removed while leaving thesecond filter assembly 502 on the second gas line 492 in place andoperational.

It is noted that although quick release couplings are used in thisembodiment, any suitable coupling, for instance screw couplings, couldbe used.

In use, both filter elements operate at the same time to filterparticulates from the exhaust gas stream. The use of two filterassemblies arranged in parallel in a gas flow circuit allows filterelements to be changed during operation of the apparatus. This isachieved by closing first and second gas circuit valves 520, 560 and gasinlet and gas outlet valves 530, 550 on one of the two filter assembliesto seal that assembly from the gas flow circuit. This sealed filterassembly is then released from the apparatus by de-coupling from thecircuit between the gas valves. The remaining filter assembly now all ofthe gas flow for the circuit.

The filter element of the removed filter assembly can either be replacedand the filter assembly returned to the apparatus, or a completely nefilter assembly can be coupled to the apparatus.

To change the filter element, the filter housing is flooded usingupstream and downstream water inlets 630, 640, as described above, toneutralize particulate matter contained within the housing. The filterhousing can then be split to safely exchange the filter element.

It is preferable that elements of the flow circuit, particularly partsof the exhaust manifold 490 or the T-junction 510, and gas valves suchas the first gas circuit gas valve 520, are independently removable bymeans of suitable joints in the circuit for cleaning and replacement.

The invention claimed is:
 1. An additive manufacturing apparatuscomprising: a build chamber, a module for providing a focused energybeam for consolidating layer-by-layer powder material in the buildchamber to build an article, a gas flow circuit for passing a flow ofgas through the build chamber during the manufacturing process, and afilter assembly, the filter assembly comprising; a filter housing havinga gas inlet and a gas outlet both said gas inlet and said gas outletbeing detachably coupled to the gas flow circuit such that the filterassembly is removably-mountable to the additive manufacturing apparatus,a particulate filter element located within the filter housing betweenthe gas inlet and the gas outlet and configured to filter at least oneof volatile and explosive powder from the gas of the gas flow circuit, afirst valve actuatable to seal the gas inlet, and a second valveactuatable to seal the gas outlet, wherein the filter housing isconfigured to allow liquid into the filter housing to flood the filterhousing for entrapping the at least one of volatile and explosive powderheld against the particulate filter element once the filter assembly hasbeen removed from the additive manufacturing apparatus and is openablefor removal of the particulate filter element, against which the atleast one of volatile and explosive powder has been entrapped by theliquid, from the filter housing after flooding of the filter housing. 2.An apparatus according to claim 1, in which the filter housingcomprises, in addition to the gas inlet, a liquid inlet for allowingliquid into the filter housing.
 3. An apparatus according to claim 1,further comprising, in addition to the gas outlet, a liquid outlet forallowing liquid to flow from the filter housing.
 4. An apparatusaccording to claim 1, in which said particulate filter element dividesthe filter housing into an upstream section and a downstream section,the filter housing comprising: a first liquid inlet allowing ingress offluid into the upstream section of the filter housing, and a secondliquid inlet allowing liquid ingress into the downstream section of thefilter housing.
 5. An apparatus according to claim 1, wherein the filterhousing comprises clamp screws for clamping the first and secondportions together.
 6. An apparatus according to claim 1, in which thefilter housing comprises a flow diverter for directing gas flow from thegas inlet to the filter element.
 7. An apparatus according to claim 1,in which the filter housing comprises first and second portionsconfigured to be separable for removal of the filter element, the firstportion comprising the gas inlet and the second portion comprising thegas outlet.
 8. An assembly according to claim 7, in which the filterelement is located by clamping between the first and second portionswith clamping screws.
 9. An apparatus according to claim 1, in which thegas flow circuit comprises a gas circuit valve actuatable to seal thecircuit upstream from the filter assembly prior to removal of theassembly.
 10. An apparatus according to claim 1, in which the gas flowcircuit further comprises a gas circuit valve actuatable to seal the gasflow circuit downstream from the filter assembly prior to removal of theassembly.
 11. An apparatus according to claim 1, wherein the filterassembly is removed from the additive manufacturing apparatus in asealed state.
 12. A method of changing a particle filter element locatedwithin a filter housing mounted on an additive manufacturing apparatus,the additive manufacturing apparatus comprising: a build chamber, amodule for providing a focused energy beam for consolidatinglayer-by-layer powder material in the build chamber to build an article,a gas flow circuit for passing a flow of gas through the build chamberduring the manufacturing process, and a filter assembly comprising: thefilter housing having a gas inlet and a gas outlet, a first valveactuatable to seal the gas inlet, and a second valve actuatable to sealthe gas outlet, wherein the gas inlet and gas outlet are detachablycoupled to the gas flow circuit such that the filter assembly isremovably-mounted to the additive manufacturing apparatus and permit gasflow through the filter housing from the gas inlet to the gas outletsuch that the filter element is configured to filter at least one ofvolatile and explosive powder from the gas of the gas flow circuit, themethod comprising, in order: (a) closing the first valve to seal the gasinlet to the filter housing and closing the second valve to seal the gasoutlet from the filter housing, (b) removing the filter assembly fromthe additive manufacturing apparatus, (c) connecting a source of liquidto the filter housing to flood the filter housing to entrap the at leastone of volatile and explosive powder held against the filter element,and (d) opening the filter housing to remove the filter element, againstwhich the at least one of volatile and explosive powder has beenentrapped by the liquid, from the filter housing.
 13. A method accordingto claim 12, comprising replacing the filter element.
 14. A methodaccording to claim 12, comprising providing a device to restrictback-flow of liquid to the source of liquid.
 15. A method according toclaim 12, wherein the filter housing is flooded with the liquid suchthat such that the at least one of volatile and explosive powder in thefilter housing is trapped in the liquid and do not escape to air.
 16. Amethod according to claim 12, wherein, in step (b), the filter assemblyis removed from the additive manufacturing apparatus in a sealed state.17. A method of changing a particle filter element located within afilter housing mounted on an additive manufacturing apparatus, theadditive manufacturing apparatus comprising: a build chamber, a modulefor providing a focused energy beam for consolidating layer-by-layerpowder material in the build chamber to build an article, a gas flowcircuit for passing a flow of gas through the build chamber during themanufacturing process, and first and second filter assemblies, each ofthe first and second filter assemblies comprising: a filter housinghaving a gas inlet and a gas outlet, and the particle filter elementlocated within the filter housing between the gas inlet and the gasoutlet and configured to filter at least one of volatile and explosivepowder from the gas of the gas flow circuit, wherein, the first andsecond filter assemblies are arranged in parallel in the gas flowcircuit of the apparatus, the method comprising: for one of the firstand second filter assemblies, providing a neutralised particle filterelement by trapping the at least one of volatile and explosive powderheld on the filter element to neutralise the at least one of volatileand explosive powder, and removing the neutralised particle filterelement from the filter housing during operation of the additivemanufacturing apparatus, wherein during removal of the neutralisedfilter element, the other of the first and second filter assemblies isused to filter the at least one of volatile and explosive powder fromthe gas of the gas flow circuit.
 18. A method according to claim 17,comprising entrapping the at least one of volatile and explosive powderheld on the filter element by flooding the filter housing before removalof the neutralised filter element from the filter housing.
 19. A methodaccording to claim 17, further comprising removing the one of the firstand second filter assemblies in a sealed state before the providingstep.
 20. An additive manufacturing apparatus comprising: a buildchamber, a module for providing a focused energy beam for consolidatinglayer-by-layer powder material in the build chamber to build an article,a gas flow circuit for passing a flow of gas through the build chamberduring the manufacturing process and a filter assembly, the filterassembly comprising: a filter housing having a gas inlet and a gasoutlet detachably coupled to the gas flow circuit, a particulate filterelement located within the filter housing between the gas inlet and thegas outlet and configured to filter at least one of volatile andexplosive powder from the gas of the gas flow circuit, a valveactuatable to seal the gas inlet, and a valve actuatable to seal the gasoutlet, wherein the filter housing is configured to allow ingress offluid into the filter housing for entrapping the at least one ofvolatile and explosive powder held on the particulate filter element toprovide a neutralized particulate filter element and openable to allowdirect access to the neutralized particulate filter element, on whichthe at least one of volatile and explosive powder is entrapped by thefluid, for removal of the neutralized particular filter element from thefilter housing.
 21. An apparatus according to claim 20, wherein thefilter housing is detached from the gas flow circuit in a sealed stateduring ingress of fluid into the filter housing for entrapping the atleast one of volatile and explosive powder held on the particulatefilter element.
 22. A method of changing a particle filter elementlocated within a filter housing mounted on an additive manufacturingapparatus, the additive manufacturing apparatus comprising: a buildchamber, a module for providing a focused energy beam for consolidatinglayer-by-layer powder material in the build chamber to build an article,a gas flow circuit for passing a flow of gas through the build chamberduring the manufacturing process, and a filter assembly comprising: afilter housing having a gas inlet and a gas outlet, and a particulatefilter element located within the filter housing between the gas inletand the gas outlet and configured to filter at least one of volatile andexplosive powder from the gas of the gas flow circuit, the methodcomprising: providing a neutralised filter element by entrapping the atleast one of volatile and explosive powder held on the particulatefilter element in a fluid to neutralise the at least one of volatile andexplosive powder, and removing the neutralised particulate filterelement, on which the at least one of volatile and explosive powder isentrapped by the fluid, from the filter housing.
 23. A method accordingto claim 22, further comprising removing the filter assembly in a sealedstate before the providing step.
 24. An additive manufacturing apparatuscomprising: a build chamber, a module for providing a focused energybeam for consolidating layer-by-layer powder material in the buildchamber to build an article, a gas flow circuit for passing a flow ofgas through the build chamber during the manufacturing process, and afilter assembly comprising: a filter housing having a gas inlet and agas outlet detachably coupled to the gas flow circuit such that thefilter assembly is removably-mountable to the additive manufacturingapparatus, a particulate filter element located within the filterhousing between the gas inlet and the gas outlet and configured tofilter at least one of volatile and explosive powder from the gas of thegas flow circuit, a first valve actuatable to seal the gas inlet, and asecond valve actuatable to seal the gas outlet, wherein the filterassembly is removable with the gas inlet sealed by the first valve andthe gas outlet sealed by the second valve such that the particulatefilter element is sealed from exposure to air within the filter housing.25. An apparatus according to claim 24, wherein the filter assembly isremoved from the additive manufacturing apparatus in a sealed state.